Electrolytic cell including a flexible sheet covering the cell base

ABSTRACT

A flexible heat-resistant elastomeric sheet particularly for an electrolytic chlorine cell of the diaphragm type and the method of making the sheet. The sheet is comprised of a vulcanized heatresistant blend of a first vulcanized rubbery polymer which will soften under the prolonged influence of heat and a second vulcanized heat-resistant rubbery polymer which will harden under the prolonged influence of heat. The first polymer preferably is polyisoprene and the second polymer is preferably a polymer of halogenated butyl rubber or ethylene propylene terpolymer rubber. The sheet is particularly useful for providing a seal and cover for the conductive base of the cell.

United States Patent [191 Custer et al.

111 3,857,775 Dec. 31, 1974 ELECTROLYTIC CELL INCLUDING A FLEXIBLE SHEET COVERING THE CELL BASE Inventors: Harry S. Custer, Barberton; Brian H. Oliver, Cuyahoga Falls, both of Ohio The Goodyear Tire & Rubber Company, Akron, Ohio Filed: June 18, 1973 Appl. No.: 371,323

Related US. Application Data Continuation-in-part of Ser. No. 251,751, May 9, 1972, abandoned.

Assignee:

US. Cl 204/252, 204/242, 204/266, 204/279, 260/3.3, 260/5 Int. Cl BOlk 3/10 Field of Search 204/252, 266, 279, 242; 260/3.3, 4 R, 5, 888

References Cited UNITED STATES PATENTS 9/1949 Sarbach ..260/5X 2,809,372 10/ i957 Frederick et al. 260/5 3,028,346 4/1962 Lemiszka et a1 260/888 X 3,743,592 7/1973 Metcalfe 204/266 Primary Examiner-John H. Mack Assistant Examiner-W. I. Solomon Attorney, Agent, or FirmF. W. Brunner; R. P. Yaist [5 7 ABSTRACT A flexible heat-resistant elastomeric sheet particularly for an electrolytic chlorine cell of the diaphragm type and the method of making the sheet. The sheet is comprised of a vulcanized heat-resistant blend of a first vulcanized rubbery polymer which will soften under the prolonged influence of heat and a second vulcanized heat-resistant rubbery polymer which will harden under the prolonged influence of heat. The first polymer preferably is polyisoprene and the second polymer is preferably a polymer of halogenated butyl rubber or ethylene propylene terpolymer rubber. The sheet is particularly useful for providing a seal and cover for the conductive base of the cell.

13 Claims, 3 Drawing Figures ELECTROLYTIC CELL INCLUDING A FLEXIBLE SHEET COVERING THE CELL BASE CROSS REFERENCE TO RELATED APPLICATION This application is a continuation-in-part of application Ser. No. 251,751 filed on May 9, 1972 now abancloned.

BACKGROUND OF THE INVENTION This invention relates to a flexible non-conductive sheet used in an electrolytic chlorine cell particularly of the diaphragm type and more specifically this invention relates to a flexible vulcanized sheet to provide a seal and cover for the base of such an electrolytic cell. This invention even more specifically relates to such a sheet having improved heat-resistant properties.

Diaphragm-type cells conventionally have included an outer steel shell or can either of a cylindrical or rectangular configuration which supports a foraminous or perforated metallic cathode constituting the cathode assembly. A fluid permeable diaphragm of asbestos material overlays the cathode to permit the brine solution contained in the anode compartment to flow or percolate through the diaphragm and cathode into the cathode chamber. The diaphragms and cathodes are usually arranged vertically but may also be disposed horizontally. The anodes conventionally take the form of flat vertically disposed blades of graphite which have been inserted into slots formed by a plurality of conductive copper metal grids which are mounted on the cell base. The grid members and the anodes are electrically connected to each other and are usually secured through the base by an electrically conductive bonding layer of lead. An electrically insulating layer or coating of a material such as asphalt is then applied over the electrically conductive bonding layer and a layer of concrete is finally applied over the asphalt layer to complete the base construction. A detailed description of an electrolytic cell of the type described is given in US. Pat. No. 2,987,463 issued on June 6, 1971 to J. C. Baker, et al. In addition, a complete discussion of the construction and operation of a diaphragm type cell can be found in the Encyclopedia of Chemical Technology, Second Edition, Vol. 1 (1963) on Pages 681-687.

Recently the conventional graphite anodes have been replaced by the development of dimensionally stable anodes. Consequently, it has become necessary to provide diaphragm-type electrolytic cells having a cell base of a more simple construction suitable for use with dimensionally stable anodes. US. Pat. No. 3,591,483 issued July 6, 1971 to R. E. Loftfield, et al., discloses a diaphragm-type electrolytic cell having improved cell based constructions in which a single sheet of at least one electrically non-conductive material such as neoprene rubber covers the entire cell base and serves to provide a compressible seal between the anodes and the cell base and between the cell base and the brine solution contained in the cell can. The sheet and the cell base are provided with aligned holes for the receipt of anode risers which extend through these holes in the non-conductive sheet and the cell base and are fastened on the bottom of the cell base by suitable means such as a nut. Each riser is provided with a flange or collar which upon tightening of the nut, forms a hydraulic seal with the non-conductive sheet, thereby preventing leakage of the brine solution or solution of electrolyte onto the cell base.

Although neoprene rubber has proven to be a suitable material for providing a seal and cover for the conductive base for limited periods of time, it has not been completely satisfactory over long periods of time. Often the elastomeric sheet has become hard and brittle due to the relatively high temperatures to which the sheet is subjected. These temperatures range from about to F on the face of the sheet in contact with the brine or electrolyte solution and from about 180 to 250F on the opposite face of the sheet which is in contact with the conductive copper or aluminum base of the cell. A particular problem occurs at the juncture between the sheet and the anode riser and at the area of contact between the outer upwardly facing surface of the sheet and the flange of the anode riser at which locations the elastomeric material becomes hard and brittle causing cracks which result in the seepage of the brine solution through the sheet and onto the conductive base of the cell. This condition results in the rapid corrosion of the copper or aluminum cell base. Furthermore, the high temperatures also cause the condition known as cavitation in which the elastomeric material erodes resulting in the creation of deep voids or cavities around the juncture of the sheet and the anode riser flange thereby preventing the proper sealing of the cell base.

OBJECTS OF THE INVENTION It is therefore a primary object of the present invention to provide an improved non-conductive. sheet for use as a seal and cover in a diaphragm electrolytic cell of the type described and also to provide a method of making such a sheet.

It is another important object of the present invention to provide an elastomeric sheet of improved heatresistant properties which will retain its flexibility after long periods of use as a seal and cover for the cell base of an electrolytic cell of the diaphragm type.

It is still another object of the present invention to provide an elastomeric sheet of improved heat-resistant composition for use in an electrolytic cell of the diaphragm type employing dimensionally stable anodes.

Other objects and advantages of this invention will become apparent hereinafter as the description thereof proceeds, the novel features, arrangements and combi' nations being clearly pointed out in the specification as well as the claims thereunto appended.

In accordance with the present invention, it has been found that the above objects are accomplished in an electrolytic cell for the production of chlorine of the diaphragm type which includes a cell can for containing a brine solution, a conductive metal cell base supporting the can and anode members disposed within the can and extending through the base by providing a flexible heatresistant elastomeric sheet covering and in contact with the cell base and subjected to the heat generated by the conductive metal of the cell base. The sheet is comprised of a vulcanized heat-resistant blend of a first vulcanized rubbery polymer which will soften under the prolonged influence of heat and a second vulcanized heat-resistant rubbery polymer which will harden under the prolonged influence of heat with the sheet due to the combined effects of said first and second polymers, thereby retaining its flexible resilient characteristics to provide a seal between the anode member and the cell base and between the cell base and the brine solution contained in the can.

The first polymer is preferably a polyisoprene selected from the group consisting of natural rubber and synthetic rubber of a cis-l,4-polymer of isoprene and the second polymer is preferably at least one heatresistant rubbery polymer selected from the group consisting of halogenated butyl rubber, ethylene propylene terpolymer rubber, a copolymer of butadiene and acrylonitrile, a copolymer of butadiene and styrene and a chlorosulfonated polyethylene. It is preferred that the weight ratio of polyisoprene to the heat-resistant polymers be from about 35/65 to about 65/35. In a preferred embodiment of the invention the second polymer is at least one polymer selected from the group consisting of chlorinated butyl rubber, brominated butyl rubber and ethylene propylene terpolymer rubber. In an even more preferred embodiment of the invention, the second polymer is chlorinated butyl rubber or ethytlene propylene terpolymer rubber. In this case the weight ratio of polyisoprene to the chlorinated butyl rubber is from about 45/55 to about 55/45 and the weight ratio of polyisoprene to the ethylene propylene terpolymer rubber is from about 35/65 to about 45/55.

In accordance with the present invention, it has also been found that a method of making a flexible heatresistant sheet of the type described comprises (a) combining the first vulcanized rubber polymer with the second heat-resistant rubbery polymer to form a heatresistant vulcanized blend of the first and second polymers, and (b) forming the blend into a flexible heatresistant sheet.

It is to be understood that for the purposes of this invention, the term vulcanized is used in its broadest sense to include all means of cross-linking rubbery polymers both with and without the use of sulfur. It is also to be understood that by vulcanized blend is meant the covulcanization of each component or polymer of the blend.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings: I

FIG. 1 is a perspective view of the flexible vulcanized sheet of this invention prior to its installation in an electrolytic cell of the diaphragm type;

FIG. 2 is a partial side elevational view of a portion of an electrolytic cell of the diaphragm type taken along its length with parts broken away to show a section through the flexible vulcanized sheet in its installed position in the cell; and

FIG. 3 is an enlarged sectional view taken on line 33 of FIG. 2.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In FIG. 1 the flexible vulcanized heat-resistant sheet or blanket l of the present invention is shown in its uninstalled condition. In this instance, the sheet 1 has a generally rectangular configuration and preferably is comprised of but a single layer of vulcanized elastomeric or polymeric material. The sheet 1, when installed in a diaphragm type cell 2, is shown in FIG. 2. The sheet 1 includes a plurality of circular uniformly positioned holes 3 which have been punched or cut out of the sheet after vulcanization or which alternately may be formed during a molding or vulcanizing process. The anode members 4 of the cell 2 shown in FIG. 2 will be inserted through these holes 3 as will be hereinafter described. The exact number and specific location of each hole, of course, will depend upon the particular construction of the cell in which the sheet is installed. The holes, for example, may have a diameter of about 1.25 inch.

The sheet 1 preferably includes a strip 5 of elastomeric material disposed on its upper or brine side surface 6 which extends around the outer periphery of the sheet 1. The strip 5 is, for example, of a semicircular cross-sectional configuration to provide a half round O-ring seal. The strip 5 may be an extrusion of either the same or a different elastomeric material as the sheet 1 which is adhered to the sheet by means of a suitable adhesive or may be molded as an integral part of the sheet if desired. In addition, another similar strip 7 of elastomeric material preferably is also provided at the lateral edges around three sides of the periphery of the lower or base side surface 8 of the sheet 1 extending over and protecting the peripheral edges of the cell base 9 on these three sides. The strip 7 ordinarily must be omitted on the lower surface of the side of the cell base 9 (not visible in the drawings) which is connected to a source of electrical power since the base plate 9 ordinarily extends beyond the edge of the sheet 1 at this location and is not covered thereby. Hence, no protective strip 7 is necessary. The strip 7 may be provided in the same manner as the sealing strip 5. An additional strip 5' of elastomeric material may be provided on the surface 6 of the sheet 1 for added sealing protection on the side of the sheet that does not include the strip 7.

As shown in FIG. 2, the cell 2 is, for example, of a construction disclosed in U.S. Pat. No. 2,987,463 and only the principle parts of the cell necessary for an understanding of the present invention will be discussed herein. The cell includes an outer shell or cell can 10 constructed of two spaced metal plates 11 and 12. The cell can 10 contains a brine 13 or electrolyte solution. The cell can 10 rests on the strip 5 which serves as a gasket to seal the inner periphery of the can. A small amount of a soft sealing material such as chemically inert putty (not shown) is normally provided adjacent to the inside of the strip 5 to insure the integrity of the seal. Cathodes 14 in the form of parallel hollow fingers constructed of perforated metal plate or metal screen project horizontally from opposite sides of the cell can 10 and are electrically joined thereto by means of welds on at least one side of the cell can (not shown). Fluid permeable diaphragms 15 of asbestos material or the like overlay or are deposited upon the cathodes 14. The cathodes l4 alternate with anode members 4 which are flat vertically disposed blades of dimensionally stable material such as platinum group'metals and alloys of platinum group metals. A more complete list of acceptable dimensionally stable material may be found in U.S. Pat. No. 3,591,483 in Columns 4 and 5.

The anode members as shown in FIG. 2 include anode risers l6 welded to the anode 4 and composed of similar dimensionally stable material. The anode risers 16 are inserted through the holes 3 in the sheet 1 and extend through the cell base 9 which is constructed of an electrically conductive material such as copper or aluminum plate provided with holes 17 that are aligned with the holes 3 of the sheet 1 to receive the anode risers. A power supply (not shown) is attached directly to the cell base 9. The anoder risers 16 extend beneath the base plate and are fastened on the bottom of the cell base 9 by means of a nut 18. The anode riser 16 includes a flange or collar 19 which contacts the outer surface of the sheet 1. The anode'riser l6 typically has a diameter of about 1.25 inch and the combined diameter of the flange 19 and riser 16 is about 2 inches.

The sheet or blanket 1 covers substantially the entire surface of the cell base 9 with the strip 7 serving as a protective lip to prevent brine or water from getting between the sheet l and the cell base 9.

During the operation of the cell, the sheet is subjected to severe conditions of stress and temperature. As shown in FIG. 3, the portion 20 of the sheet in contact with the collar 19 of the anode riser 16 is compressed as much as 25 percent upon tightening of the nut 18. For example, a sheet having a thickness of about onefourth of an inch may be compressed to a thickness of about three-sixteenths of an inch resulting in the creation of stress areas around the hole 3. The upwardly disposed surface 6 of the sheet 1 is in direct contact with the brine solution 13 contained in the cell can 10 which is of a temperature of from about 180F to about 190F. Moreover, the temperature of the power receiving cell base 9 which contacts the downwardly disposed surface 8 of the sheet 1 has been measured at from 180 to 250F. It is considered that the sheet 1 is subjected to a constant temperature of'about 200F during the operation of the cell 2. Furthermore, the brine solution 13 contains corrosive substances such as chlorine which will attack the elastomeric material of the sheet 1. Previously, sheets comprised of elastomeric material such as neoprene rubber have failed prematurely in service due to these severe conditions. A particular location of such failures has been at the area of the anode receiving holes 3. Sheets which have been removed from the cells after prolong exposure to the above-described conditions have shown visible evidence of both heat cracking and erosion due to the condition known as cavitation. These defects result in the seepage of brine through the non-conductive sheet onto the conductive cell base causing corrosion and hot spots to develop in the cell base material resulting in the cell being removed from service. A particular problem in this regard has arisen at the juncture of the anode riser collar 19 and the portion 20 of the face or surface 8 of the sheet disposed under the collar 19 at which location the elastomeric material becomes hard and brittle causing the occurrence of the ab0vedescribed defects.

In accordance with this invention, the sheet 1 is comprised of a vulcanized blend of a first vulcanized heatresistant rubbery polymer which will soften under the prolonged influence of heat and a second vulcanized heat-resistant rubbery polymer which will harden under the prolonged influence of heat. The combined reaction of the first and second polymers apparently have the affect of counter-balancing each other resulting in an elastomeric sheet having properties of hardness, resiliency and flexibility approaching that of the original sheet. The sheet will thereby retain at least a high level of its desirable scalability properties resulting in the development of fewer cracks and a resistance to cavitation.

It has been determined that the sheet when tested according to the method prescribed by the American Society for Testing and Materials (ASTM D-573) for 7 days at F will exhibit a hardness increase of less than 10 points as measured on the Shore A scale. Preferably this increase in hardness is less than 7 points.

In the practice of this invention, one heat-resistant polymer which will soften under the prolonged influence of heat is a polyisoprene selected from the group consisting of natural ruber or synthetic rubbers of a cis- 1,4polymer of isoprene known as synthesized natural rubber which may contain up to 15 percent of the trans polymer and which are similar to natural rubber in structure and use.

The natural rubber that can be used is any of the well-known types such as pale crepe and smoke sheet, chemically treated natural rubber or balata. It is preferred in the practice of this invention that the natural rubbers be of a high cis-polyisoprene such as pale crepe and smoked sheet which exhibit a high degree of flexibility.

It has been found that polyisoprene polymers of the type described, when properly compounded, will soften under the prolonged influence of heat and will exhibit good scalability properties by retaining their resiliency and flowability. Furthermore, it is well known that polyisoprene polymers have a high resistance to the permeation and attack of chlorine which is present in at least small amounts in the brine or electrolyte solution.

In accordancewith the invention, aheat-resistant polymer which will harden under the prolonged influence of heat is at least one halogenated butyl rubber polymer selected from the group consisting of chlorinated butyl and brominated butyl rubber. The halogenated butyl rubbers or halobutyl rubbers as they are sometimes called are well known in the art being pre pared normally by the halogenation of butyl rubber, a well-known polymer containing a major portion of bound isobutylene, e.g., from about 85 to 99.5 weight percent, and a minor portion of isoprene, e.g., from about 15 to 0.5 weight percent. Halobutyl rubbers include chlorobutyl as well as bromobutyl rubber. Descriptions of halobutyl rubber and its preparation appear in the US. Pat. No. 3,242,148, the revelations of which are incorporated herein by reference. In chlorobutyl rubber typically the chlorine content is less than 3 percent by' weight normally being from about 1.1 to about 1.3 weight percent. Normally about percent of the unsaturation in the original butyl rubber is retained on chlorination, the unsaturation usually being from about 1.1 to about 1.7 percent. A typical molecular structure of Enjay Butyl HT Polymer is shown as follows:

l l 01 LC H3 5000 Cl The compounding and vulcanization of chlorobutyl rubber is well known; see U.S,. Pat. No. 3,197,446, the disclosures of which are incorporated herein by reference. Sulfur and accelerator combinations or zinc oxide, zinc chloride, diamines and dithiols are examples of compounds which can be used in the vulcanization of halobutyl rubber. Bromobutyl rubber is similar to chlorobutyl rubber, the main difference being that it contains bromo groups rather than chloro groups. Butyl rubbers containing both chloro and bromo groups can also be used.

Halogenated butyl rubbers are also described in the Encyclopedia of Chemical Technology, Second Supplement Volume, edited by Raymond E. Kirk and Donald F. Othmer, The lnterscience Encyclopedia, Inc., New York, pages 716 to 734, and the Encyclopedia of Polymer Science and Technology, Vol. 2, lnterscience Publishers, a division of John Wiley & Sons, Inc., New York, London, Sidney, pages 762 763, 771, 772 and 782. The revelations of these references are incorporated herein by reference.

It has been determined that a vulcanized blend or covulcanization of a polyisoprene polymer and a polymer of halogenated butyl rubber will provide a composition for the non-conductive vulcanized elastomeric sheet which when installed in an electrolytic cell, will exhibit an improved resistance to the severe conditions present in the cell. It is preferred that the weight ratio of polyisoprene to the halogenated polymer be from about 35/65 to about 65/35. In preferred form of the invention, a rubbery polymer of chlorinated butyl rubber is blended with a rubbery polymer of polyisoprene and the weight ratio of the polyisoprene to the chlorinated butyl rubber in the vulcanized blend is from about 45/55 to about 55/45.

In the practice of the invention, a rubber polymer of brominated butyl rubber, ethylene propylene terpolymer rubber, a copolymer of butadiene and acrylonitrile, a copolymer of butadiene and styrene, or a chlorosulfonated polyethylene may also be blended with a rubber polymer of polyisoprene and covulcanized with equivalent results. In this regard, the use of a rubbery polymer of ethylene propylene terpolymer rubber is most preferred to achieve the most satisfactory results with the ratio of the polyisoprene to the ethylene propylene terpolymer being from about 35/65 to about 45/55.

The ethylene propylene terpolymers which may be used in accordance with the present invention are terpolymers-of ethylene, propylene and non-conjugated dienes (EPDM). Representative examples of these rubbery terpolymers are described in U.S. Pat. No.

3,331,793, Column 2, lines 54-59.

The copolymers of butadiene and acrylonitrile commonly referred to as nitrile rubber which may be used in the practice of the present invention are a vulcanized rubbery copolymer of butadiene and acrylonitrile of the type disclosed in Rubber Chemistry and Technology A rubber review for 1963 nitrile rubber by W. Hofmann," Volume 37 April-June 1964, Part 2. In the nitrile rubbers which may be used in the present invention preferably the acrylonitrile is present in an amount of at least 25 percent of the total copolymer with'the amount of acrylonitrile in the copolymers of the present invention being normally from 25 percent to about 60 percent.

The copolymers of butadiene and styrene which may be used in the practice of the present invention are the butadiene 1,3/styrene elastomers (SBR) well known in the art. These polymers normally possess a bound butadiene content of at least 40 weight percent and preferably at least 50 weight percent, most preferably at least 70 weight percent.

The chlorosulfonated polyethylenes which can be used in the present invention are solid polymers and are well known in the art. They possess a chlorine content of to 50 percent, preferably 25 to 50 percent, more preferably 25 to 30 percent, and most preferably 28 to 30 percent. They can be prepared by the chlorination of polyethylene and reacting the polymer with the sulfur dioxide to introduce sulfonyl chloride groups. These polymers are described in U.S. Pat. Nos. 2,212,786; 2,586,363; 2,646,422; 2,862,917; 2,879,261; 2,972,604 and 2,982,759. The sulfur content of the polymers due to the sulfonyl groups is from 0.40 to 3.0 percent, preferably 0.70 to 3.0 percent and most preferably 1.0 to 1.5 percent. A typical polymer has a molecular weight of about 20,000; a specific gravity of about 1.11 to 1.28 and a raw polymer viscosity of 30 to 66 (ML-4 at 212F).

It is to be understood that various vulcanizing agents well known in the art may be used to'cure or vulcanize (covulcanize) the blend used in the practice of the present invention. Representative examples of the vulcanizing agents are: vulcanizing agents of the peroxide type (except for polymers of halogenated butyl rubber), such as dicumyl peroxide, or of the nitroso compound type, or sulfur and the sulfur-containing agents such as benzothiazole d'isulfide, tetramethyl thiuram disulfide, 4,4-dithiodimorpholine, 4-morpholino-2 benzothiazole disulfide, or diphenyl guanidine. Activators well known in the art such as zinc oxide, magnesium oxide and stearic acid should also be used to enhance the cure. v

Various additivies, fillers, plasticizers and pigments can also be added to the polymers of the present invention. Examples of such material are: carbon blacks, particular of the fast extruding furnace and high abrasion furnace types, and plasticizers such as petroleum oils, naturally occurring and synthetic ester oils, and resinous polymers of thenaturally occurring and synthetic types.

The method of making the flexible vulcanized sheet 1 of the present invention to be used in an electrolytic cell of the diaphragm type for the production of chlorine includes compounding the heat-resistant formulation by combining the polymers in the preferred proportions as discussed above to form a heat-resistant rubbery vulcanized blend. This can be accomplished by conventional mixing techniques using conventional rubber processing equipment such as a Banbury mixer or mixing mill. Equivalent results are obtained with internal Banbury mixed formulations and mill mixed formulations. Curatives may be added during either a first or a second pass in the Banbury mixer or separately on a mixing mill. The rubber blend of the heat-resistant polymers is then formed into a vulcanized sheet in a conventional manner for example by using a rubber calender or extruder to form the sheet into the desired dimensions and by thereafter vulcanizing or curing the formed sheet by means of a curing press rotocure, autoclave or hot air oven. After vulcanization, the anode receiving holes 3 and the elastomeric strips 5, 5' and 6 are provided in a manner as previously described.

The following examples further illustrate the objects and advantages of this invention.

EXAMPLE 1 A flexible vulcanized elastomeric sheet 1 of the type shown in FIGS. 1'-3 was manufactured having the following composition:

Components Parts by Weight Polyisoprene (1) 55.00 Chlorobutyl Rubber (2) 45.00 Magnesium Oxide 1.00 Non-Black Filler 5.00 Carbon Black 65.00 Stearic Acid 2.00 Antioxidant 1.00 Paraffin Wax 1.00 Plasticizer 6.00 Zinc Oxide 5.00 Vulcanizing Agents 2.80

TOTAL 188.80

(I) Obtained as Natsyn 400. Sold by The Goodyear Tire & Rubber Company. (2) Enjay Butyl HT 1066 Polymer.

zinc oxide and the vulcanizing agents were added to a Banbury mixer and mixed to produce a nonproductive stock. The zinc oxide and vulcanizing agents were then added to the non-productive stock in the Banbury during a second pass mixing procedure.

After the mixing procedure was complete, samples were taken from the composition and were tested for original and heat-aged physical properties. The results of these tests were given in Table I below. The samples were compression molded in a vulcanizing press at 365F at the times listed below in Table I.

Oven Age 168 Hrs at 212F (ASTM D-573) Ultimate Tensile (psi) 850 800 800 Elongation 290 280 310 Durometer Hardness (Shore A)* 64 64 64 Average of two sheets. Average of three sheets.

The above data contained in Tables 1 and II illustrate that the heat-resistant composition may be used over a wide range of cure from 305 to 365F. Even though the original physical properties showed deterioration as the result of heat aging, the durometer hardness remained substantially constant demonstrating the heatresistant properties of the composition of this invention.

The above composition was then processed on a roller die extruder and formed into a rectangular sheet or web of material having a gauge or thickness of onefourth of an inch. The sheet was next rolled into a polyethylene liner. The roll was cured in a rotocure at a temperature of 340F for 17 minutes. After vulcanization, the sheet 1 is prepared for installation in an electrolytic cell 2 of the type shown in FIG. 2 by being cut and trimmed to size. The sheet has, for example, a width of inches, a length of 69% inches and a gauge of one-fourth of an inch. Holes 3 for receiving the anode risers 16 are punched in this sheet with the holes 3 being disposed, for example, in equally spaced rows with an equal number of holes in each row. The holes 3, for example, may have a diameter of about 1.25 inch. The sheet is then provided with extruded strips 5, 5' and 6 of neoprene rubber adhered to the sheet in the locations shown in FIG. 1 by means of commercially available neoprene contact adhesive. in this regard, however, it should be appreciated that the strip may (Shore A) Average 01' two sheets. Average of three sheets.

Another group of samples were obtained and were tested for the same physical properties as presented in Table l. The results of these tests were given below in Table 11. The samples were compression molded in a vulcanizing press at 305F at the time shown below in Table 11.

TABLE II Original-Cure at 305F 30 min 40 min min (ASTM D-412) also be of the same composition as the sheet 1 indicated above with other suitable adhesives being used.

The sheet is then installed in an electrolytic cell 2 as shown in FIG. 2 of the type described in U.S. Pat. No. 2,987,463 (Hooker type S-3) except having a cell base construction as described in U.S. Pat. No. 3,591,483. The installation includes placing the sheet 1 on a copper base plate 9 so that the holes 3 in the sheet 1 are aligned with an equal number of holes 17 in the base 9. Then dimensionally stable anodes 4 are set in place with anode risers 16 having a diameter of about 1.25 of an inch being inserted through the anode-receiving holes 3 of the sheet 1. The anode risers 16 are bolted to the bottom side of the copper base plate 9 and the collar or flange 19 of the riser 16 is seated against the upwardly disposed surface 6 of the sheet 1 with the combined diameter of the flange 19 and riser 16 being about two inches. The nut 18 at the bottom of the cell base 9 is tightened so that the sheet 1 is compressed from a diameter of about one-fourth of an inch to a diameter of about three-sixteenths of an inch. After the installation of the cell base 9, the cell can 10, cathodes 14 and diaphragms 15 are fitted in place to complete the assembly of the cell 2.

The cell 2 is then fed with a brine solution 13 and operated under general conditions of the type described in the example provided in U.S. Pat. No. 3,591,483,

5 Samples of Compositions A-E were tested along with a sample of a commercial grade sheet of a basically neoprene composition of the type previously used in electrolytic cells of the diaphragm type. The neoprene sheet was labeled as Composition F. The results of the Column 8. After several months of service the sheet e ts are listed below:

had shown no visible signs of heat cracking or cavitation.

EXAMPLE 2 A sample sheet having the same composition as the sheet of Example 1 was manufactured in the same manner as described in Example 1 except that the sheet had a length and width of 12 inches and a thickness of onefourth of an inch. A donut-shaped test sample was punched out of this sample sheet having an outside diameter of two and one-halfinches and an inside diameter of one and three-eighths inches. This sample was positioned between two titanium metal discs each also having an outside diameter of two and one-half inches and an inside diameter of one and three-eighths inches.

The discs were clamped together with the sample being compressed about 25 percent to a thickness of about three-sixteenths of an inch to simulate the compression the non-conductive sheet undergoes in actual service in a diaphragm type cell. The above assembly was immersed inthe brine solution of a commercial electrolytic cell of the diaphragm type having a cell base construction as described in U.S. Pat. No. 3,591,483. The cell was operated'under general conditions of the type described in the example provided in Column 8 of this patent. After several months of immersion in the brine solution of the cell, the sample has had no reported defects.

EXAMPLE 3 In order to test the hardness increase under heat aging conditions, samples of vulcanized elastomeric sheets of various compositions were tested in accordance with ASTM D-573. Compositions A, B and C were comprised of the vulcanized blend of the present invention in the proportions indicated below. Compositions D and E were comprised of conventional rubbery polymer formulations of polyisoprene and chlorobutyl rubber respectively.

In compositions A, B, C and E the same plasticizers, fillers and vulcanizing agents were used as are discussed in Example 1. In Composition D the same plasticizers and fillers were used also but the vulcanizing The above data indicates that the hardness increase upon heat aging of Compositions A, B and C which were comprised of a heat-resistant vulcanized blend of polyisoprene and chlorobutyl rubber was, less than for Composition D comprised of a polyisoprene polymer and Composition E comprised of a chlorobutyl polymer. In this regard, based on facts well known to those skilled in the art, Composition D may be expected to increase further in hardness and then to revert causing a decrease in hardness and a general degradation of properties until an ultimate failure occurs and Composition E will continue to increase in hardness until a point of ultimate failure. The increase in hardness is realized by the use of Compositions B and C which contain a 60/40 and 55/45 ratio respectively between the polyisoprene and the chlorobutyl rubber. The data further indicates that the heat-resistant sheets of this invention exhibit a hardness change or increase of far less than that of commercially available sheets illustrated by Composition F.

In the practice of the present invention, all of the above examples can be repeated by substituting polymers of bromobutyl, ethylene propylene terpolymer,

butadiene/styrene, nitrile rubber and chlorosulfonated polyethylene for the chlorobutyl polymer with equivalent results. In this regard the substitution of ethylene propylene terpolymer is most preferred to achieve the most satisfactory results. Of course, appropriate compounding changes well known to those skilled in the art may become necessary due to the substitution.

It should be apparent to those skilled in the art that the present invention provides an improved non- Parts by Weight (1) Obtained as Natsyn 400. Sold by The Goodyear Tire & Rubber Company.

(2) Enjay Butyl HT 1066 Polymer.

conductive sheet of improved heat-resistant properties for use as a seal and cover in a diaphragm electrolytic cell of the type described.

Moreover, though the use of the flexible heatresistant sheet of this invention has been illustrated in conjunction with an electrolyte chlorine cell of the diaphragm type, it should be apparent to those skilled in the art that the vulcanized sheet may also be used in cells for the production of chlorine, for example, a mercury type electrolytic cell. In this regard, the sheet of this invention is similar in composition and structure to the flexible cover particularly suitable for a mercury type cell as disclosed in our copending application Ser. No. 251,827 entitled FLEXIBLE COVER FOR AN ELECTROLYTIC CELL filed May 9, 1972 now U.S. Pat. No. 3,794,577.

While certain representative embodiments and details have been shown for the purpose of illustrating the invention, it will be apparent to those skilled in the art that various changes and modifications may be made therein without departing from the spirit or scope of the invention.

We claim:

1. In an electrolytic cell of the diaphragm type for the production of chlorine, said cell comprising a cell can for containing a brine solution, a conductive metal cell base supporting said can and anode members disposed within said can and extending through said base; a flexible heat-resistant elastomeric sheet covering and in contact with said cell base and subjected to the heat generated by the conductive metal of the cell base, said sheet comprised of a vulcanized heat-resistant blend of a first vulcanized rubbery polymer which will soften under the prolonged influence of heat wherein said first polymer is a polyisoprene selected from the group consisting of natural rubber and synthetic rubber of a cis l,4-polymer of isoprene and a second vulcanized heatresistant rubbery polymer which will harden under the prolonged influence of heat wherein said second polymer is at least one polymer selected from the group consisting of halogenated butyl rubber, ethylene propylene terpolymer rubber, a copolymer of butadiene and acrylonitrile, a copolymer of butadiene and styrene and a chlorosulfonated polyethylene and wherein the weight ratio of said polyisoprene to said second polymer is from about 35/65 to about 65/35, said sheet, due to the combined effects of said first and second polymers, thereby retaining its flexible resilient characteristics to provide a seal between the anode member and the cell base and between the cell base and the brine solution contained in the can. I

2. The invention as claimed in claim I wherein the sheet when tested for 7 days at 250F in accordance with ASTM D573 will exhibit a hardness increase of less than 10 points as measured on the Shore A scale.

3. The invention as claimed in claim 1 wherein said halogenated butyl rubber is selected from the group consisting of chlorinated butyl and brominated butyl rubber.

4. The invention as claimed in claim 3 wherein said second polymer is at least one polymer selected from the group consisting of chlorinated butyl rubber, brominated butyl rubber and ethylene propylene terpolymer rubber.

5. The invention as claimed in claim 1 wherein said second polymer is chlorinated butyl rubber anad the weight ratio of polyisoprene to said chlorinated butyl rubber is from about 45/55 to about 55/45.

6. The invention as claimed in claim 1 wherein said second polymer is ethylene propylene terpolymer rubber and the weight ratio of polyisoprene to said ethylene propylene terpolymer rubber is from about 35/65 to about 45/55.

7. In an electrolytic cell of the diaphragm type comprising the combination of a cell can for containing a brine solution, a conductive metal cell base supporting said can, cathodes and dimensionally stable anodes disposed within the can with the anodes connected to anode risers which extend through the cell base, and an electrically non-conductive vulcanized elastomeric sheet covering substantially the entire cell base serving to provide a compressible seal between the anodes and the cell base and between the cell can and the cell base with the sheet subjected to the heat generated by the conductive metal of the cell base, the improvement wherein said sheet is comprised ofa heat-resistant vulcanized blend of a first vulcanized rubbery polymer which will soften under the prolonged influence of heat wherein said first polymer is a polyisoprene selected from the group consisting of natural rubber and synthetic rubber ofa cis l,4-polymer of isoprene and a second vulcanized rubbery polymer which will harden under the prolonged influence of heat wherein said second polymer is at least one polymer selected from the group consisting of halogenated butyl rubber, ethylene propylene terpolymer rubber, a copolymer of butadiene and acrylonotrile, a copolymer of butadiene and styrene and a chlorosulfonated polyethylene and wherein the weight ratio of said polyisoprene to said second polymer is from about 35/65 to about 65/35, said sheet, due to the combined effects of said first and second polymers, thereby retaining its flexible resilient characteristics to prevent cracking of the sheet at the juncture between the anode risers and the cell base and the resulting leakage of the brine solution onto the conductive metal of the base.

8. The invention as claimed in claim 7 wherein said sheet is comprised of at least a single layer of said first and second polymer with said layer in contact with a flanged member of said anode riser.

9. The invention as claimed in claim 7 wherein the sheet, when tested for 7 days at 250F in accordance with ASTM D-573, will exhibit a hardness increase of less than 10 points as measured on the Shore A scale.

10. The invention as claimed in claim 7 wherein said halogenated butyl rubber is selected from the group consisting of chlorinated butyl and brominated butyl rubber.

11. The invention as claimed in claim 10 wherein said second polymer is at least one polymer selected from the group consisting of chlorinated butyl rubber, brominated butyl rubber and ethylene propylene terpolymer rubber.

12. The invention as claimed in claim 7 wherein said second polymer is chlorinated butyl rubber and the weight ratio of polyisoprene to said chlorinated butyl rubber is from about 45/55 to about 55/45.

13. The invention as claimed in claim 7 wherein said second polymer is ethylene propylene terpolymer rubber and the weight ratio of polyisoprene to said ethylene propylene terpolymer rubber is from about 35/65 to about 45/55.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION PATENT NO. 1 3,857,775 DATED December 31, 197% |NVENTOR(5) 1 Harry S Custer and Brian H Oliver It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown beiow:

Column 12, line 3%, after "The" insert -least-.

Signed and Scaled this fourth Day Of Nqvember1975 [SEAL] Attest:

RUTH C. MASON C. MARSHALL DANN Arresting Officer Commissioner uj'latems and Trademarks UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION PATENT NO. 3,857,775 DATED December 31, 197"- INVENTOR(S) Harry S Custer and Brian H Oliver It is certified that error appears in the aboveidentitied patent and that said Letters Patent are hereby corrected as shown below:

Column 5, line 66,"25 F" should read 25O F Column 7, lines 25and 30, "rubber" should read rubbery-n Column 8, line 52, "rubber" should read "rubbery-w Signed and Scaled this second Day Of September 1975 [SEAL] A ttes r.-

RUTH C. MASON C. MARSHALL DANN Arresting Officer (mnmissiuncr nj'Patenrs and Trademarks 

1. IN AN ELECTROLYTIC CELL OF THE DIAPHRAGM TYPE FOR THE PRODUCTION OF CHLORINE, SAID CELL COMPRISING A CELL CAN FOR CONTAINING A BRINE SOLUTION, CONDUCTIVE METAL CELL BASE SUPPORTING SAID CAN AND ANODE MEMBERS DISPOSED WITHIN SAID CAN AND EXTENDING THROUGH SAID BASE; A FLEXIBLE HEAT-RESISTANT ELASTOMERIC SHEET COVERING AND IN CONTACT WITH SAID CELL BASE ABND SUBJECTED TO THE HEAT GENERATED BY THE CONDUCTIVE METAL OF THE CELL BASE, SAID SHEET COMPRISED OF A VULCANIZED HEAT-RESISTANT BLEND OF A FIRST VULCANIZED RUBBERY POLYMER WHICH WILL SOFTEN UNDER THE PROLONGATED INFLUENCE OF HEAT WHEREIN SAID FIRST POLYMER IS A POLYISOPRENE SELECTED FROM THE GROUP CONSISTING OF NATURAL RUBBER AND SYNTHETIC RUBBER OF A CIS 1,4-POLYMER OF ISOPRENE AND A SECOND VULCANIZED HEAT-RESISTANT RUBBERY POLYMER WHICH WILL HARDEN UNDER THE PROLONGED INFLUENE CE OF HEAT WHEREIN SAID SECOND POLYMER IS AT LEAST ONE POLYMER SELECTED FROM THE GROUP CONSISTING OF HALOGENATED BUTYL RUBBER, ETHYLENE PROPYLENE TERPOLYMER RUBBER, A COPOLYMER OF BUTADIENE AND ACRYLONITRILE, A COPOLYMER OF BUTADIENE AND STYRENE AND A CHLOROSULFONATED POLYETHYLENE AND WHEREIN THE WEIGHT RATIO OF SAID POLYISOPRENE TO SAID SECOND POLYMER IS FROM ABOUT 35/65 TO ABOUT 65/35, SAID SHEET, DUE TO THE COMBINED EFFECTS OF SAID FIRST AND SECOND POLYMERS, THEREBY RETAINING ITS FLEXIBLE REILIENT CHARACTERISTICS TO PROVIDE A SEAL BETWEEN THE CELL BASE AND BER AND THE CELL BASE AND BETWEEN THE CELL BASE AND THE BRINE BRINE SOLUTION CONTAINED IN THE CAN.
 2. The invention as claimed in claim 1 wherein the sheet when tested for 7 days at 250*F in accordance with ASTM D-573 will exhibit a hardness increase of less than 10 points as measured on the Shore A scale.
 3. The invention as claimed in claim 1 wherein said halogenated butyl rubber is selected from the group consisting of chlorinated butyl and brominated butyl rubber.
 4. The invention as claimed in claim 3 wherein said second polymer is at least one polymer selected from the group consisting of chlorinated butyl rubber, brominated butyl rubber and ethylene propylene terpolymer rubber.
 5. The invention as claimed in claim 1 wherein said second polymer is chlorinated butyl rubber anad the weight ratio of polyisoprene to said chlorinated butyl rubber is from about 45/55 to about 55/45.
 6. The invention as claimed in claim 1 wherein said second polymer is ethylene propylene terpolymer rubber and the weight ratio of polyisoprene to said ethylene propylene terpolymer rubber is from about 35/65 to about 45/55.
 7. In an electrolytic cell of the diaphragm type comprising the combination of a cell can for containing a brine solution, a conductive metal cell base supporting said can, cathodes and dimensionally stable anodes disposed within the can with the anodes connected to anode risers which extend through the cell base, and an electrically non-conductive vulcanized elastomeric sheet covering substantially the entire cell base serving to provide a compressible seal between the anodes and the cell base and between the cell can and the cell base with the sheet subjected to the heat generated by the conductive metal of the cell base, the improvement wherein said sheet is comprised of a heat-resistant vulcanized blend of a first vulcanized rubbery polymer which will soften under the prolonged influence of heat wherein said first polymer is a polyisoprene selected from the group consisting of natural rubber and synthetic rubber of a cis 1,4-polymer of isoprene and a second vulcanized rubbery polymer which will harden under the prolonged influence of heat wherein said second polymer is at least one polymer selected from the group consisting of halogenated butyl rubber, ethylene propylene terpolymer rubber, a copolymer of butadiene and acrylonotrile, a copolymer of butadiene and styrene and a chlorosulfonated polyethylene and wherein the weight ratio of said polyisoprene to said second polymer is from about 35/65 to about 65/35, said sheet, due to the combined effects of said first and second polymers, thereby retaining its flexible resilient characteristics to prevent cracking of the sheet at the juncture between the anode risers and the cell base and the resulting leakage of the brine solution onto the conductive metal of the base.
 8. The invention as claimed in claim 7 wherein said sheet is comprised of at least a single layer of said first and second polymer with said layer in contact with a flanged member of said anode riser.
 9. The invention as claimed in claim 7 wherein the sheet, when tested for 7 days at 250*F in accordance with ASTM D-573, will exhibit a hardness increase of less than 10 points as measured on the Shore A scale.
 10. The invention as claimed in claim 7 wherein said halogenated butyl rubber is selected from the group consisting of chlorinated butyl and brominated butyl rubber.
 11. The invention as claimed in claim 10 wherein said second polymer is at least one polymer selected from the group consisting of chlorinated butyl rubber, brominated butyl rubber and ethylene propylene terpolymer rubber.
 12. The invention as claimed in claim 7 wherein said second polymer is chlorinated butyl rubber and the weight ratio of polyisoprene to said chlorinated butyl rubber is from about 45/55 to about 55/45.
 13. The invention as claimed in claim 7 wherein said second polymer is ethylene propylene terpolymer rubber and the weight ratio of polyisoprene to said ethylene propylene terpolymer rubber is from about 35/65 to about 45/55. 